#include "apue.h"
#include <error.h>
#include <fcntl.h>
#include <sys/wait.h>

/*
 * Pointer to array allocated at run-time
 */
static pid_t *childpid = NULL;

/*
 * From our open_max(), {Figure 2.17}
 */
static int   maxfd;

FILE *
popen(const char *cmdstring, const char *type)
{
    int     i;
    int     pfd[2];
    pid_t   pid;
    FILE   *fp;

    /* only allow "r" or "w" */
    if ((type[0] != 'r' && type[0] != 'w') || type[1] != 0) {
        errno = EINVAL;
        return(NULL);
    }

    if (childpid == NULL) { /* first time throught */
        /* allocate zeroed out array for child pids */
        maxfd = open_max();
        if ((childpid = calloc(maxfd, sizeof(pid_t))) == NULL)
            return(NULL);
    }

    if (pipe(pfd) < 0)
        return(NULL); /* errno set by pipe() */
    if (pfd[0] >= maxfd || pfd[1] >= maxfd) {
        close(pfd[0]);
        close(pfd[1]);
        errno = EMFILE;
        return(NULL);
    }

    if ((pid = fork()) < 0) {
        return(NULL);   /* errno set by fork() */
    } else if (pid == 0) {  /* child */
        if (*type == 'r') {
            close(pfd[0]);
            if (pfd[1] != STDOUT_FILENO) {
                dup2(pfd[1], STDOUT_FILENO);
                close(pfd[1]);
            }
        } else if (*type == 'w') {
            close(pfd[1]);
            if (pfd[0] != STDIN_FILENO) {
                dup2(pfd[0], STDIN_FILENO);
                close(pfd[0]);
            }
        }

        /* close all descriptors in childpid[] */
        for (i = 0; i < maxfd; i++)
            if (childpid[i] > 0)
                close(i);
        execl("/bin/sh", "sh", "-c", cmdstring, (char*)0);
        _exit(127);
    }

    /* parent continues... */
    if (*type == 'r') {
        close(pfd[1]);
        if ((fp = fdopen(pfd[0], type)) == NULL)
            return(NULL);
    } else {
        close(pfds[0]);
        if ((fp = fdopen(pfd[1], type)) == NULL)
            return(NULL);
    }

    childpid[fileno(fp)] = pid;     /* remeber child pid for this fd */
    return(fp);
}

int
pclose(FILE *fp)
{
    int     fd, stat;
    pid_t   pid;

    if (childpid == NULL) {
        errno = EINVAL;
        return(-1);     /* popen() has never been called */
    }

    fd = fileno(fp);
    if (fd >= maxfd) {
        errno = EINVAL;
        return(-1);     /* invalid file descriptor */
    }
    if ((pid = childpid[fd]) == 0) {
        errno = EINVAL;
        return(-1);     /* fp wasn't opened by popen() */
    }

    childpid[fd] = 0;
    if (fclose(fp) == EOF)
        return(-1);

    while (waitpid(pid, &stat, 0) < 0)
        if (errno != EINTR)
            return(-1); /* error other than EINTR from waitpid() */

    return(stat);   /* return child's termination status */
}
